The present invention relates to a vibration absorber for absorbing a vibration between first and second members each of which is connected to the vibration absorber.
In a prior art vibration absorber as disclosed in JP-A-9-317815, a piston urges a liquid to move an insulator member so that a vibration transmitted to the insulator member is absorbed, and the piston is driven pneumatically.
An object of the present invention is to provide a vibration absorber for absorbing a vibration between first and second members each of which is connected to the vibration absorber, in which vibration absorber a size of the vibration absorber is decreased in comparison with the prior art.
A vibration absorber for absorbing a vibration between first and second members each of which is connected to the vibration absorber, according to the present invention, comprises, a movable member adapted to contact with a fluid, and including a portion connected mechanically to one of the first and second members so that a movement of the fluid and a movement of the portion of the movable member correspond to each other, and a fluid moving member for flowing the fluid in either or selected one of an extension direction in which the portion of the movable member moves to increase a distance between the first and second members and a contraction direction in which the portion of the movable member moves to decrease the distance between the first and second members in such a manner that the vibration is restrained by a change of the distance between the first and second members from being transmitted between the first and second member.
Since the fluid moving member flows the fluid in either or the selected one of the extension direction in which the portion of the movable member moves to increase the distance between the first and second members and the contraction direction in which the portion of the movable member moves to decrease the distance between the first and second members in such a manner that the vibration is restrained by the change of the distance between the first and second members from being transmitted between the first and second member, that is, the fluid moving member urges the fluid in the extension direction to move the portion of the movable member in the extension direction or allows the fluid to flow with a low flow resistance in the extension direction so that the portion of the movable member is allowed to move easily in the extension direction when a force of the vibration to be absorbed urges the portion of the movable member to increase the distance between the first and second members, and the fluid moving member urges the fluid in the contraction direction to move the portion of the movable member in the contraction direction or allows the fluid to flow with a low flow resistance in the contraction direction so that the portion of the movable member is allowed to move easily in the contraction direction when the force of the vibration to be absorbed urges the portion of the movable member to decrease the distance between the first and second members, a size of the fluid moving member may be small so that a size of the vibration absorber is decreased in comparison with the prior art.
It is preferable for decreasing a force for driving the fluid moving member that a reaction force generated elastically in accordance with the movement of the fluid is applicable to the fluid moving member. It is preferable for decreasing the force for driving the fluid moving member that the fluid moving member is reciprocally movable.
When the reciprocal movement of the fluid moving member resonates with a driving frequency at which the fluid moving member is driven reciprocally to flow the fluid in such a manner that the change of the distance between the first and second members for restraining the vibration from being transmitted between the first and second members is generated, the force for driving the fluid moving member is minimized to decrease the size of the vibration absorber. When a characteristic frequency of a reciprocal movement of the fluid moving member determined by a mass or moment of inertia of the fluid moving member and a spring constant of the reaction force is substantially equal to the driving frequency at which the fluid moving member is driven reciprocally to flow the fluid, the reciprocal movement of the fluid moving member resonates with the driving frequency so that the force for driving the fluid moving member is minimized to decrease the size of the vibration absorber. The spring constant is, in almost cases, a dynamic spring constant, because the fluid moving member bears a viscous resistance when being driven.
When the characteristic frequency of the fluid moving member determined by the mass or moment of inertia of the fluid moving member and the spring constant of the reaction force is slightly larger than the driving frequency at which the fluid moving member is driven reciprocally to flow the fluid in such a manner that the change of the distance between the first and second members for restraining the vibration from being transmitted between the first and second members is generated, a relatively large force for urging the portion of the movable member can be generated within a relatively wide vibration frequency range, or a force necessary for driving the fluid moving member is relatively small within the relatively wide vibration frequency range.
When the driving frequency at which the fluid moving member is driven reciprocally to flow the fluid is equal to or slightly more than a frequency of the vibration to be absorbed between the first and second members, the vibration is effectively absorbed in the relatively wide vibration frequency range.
It is preferable for generating the resonant reciprocal movement of the fluid moving member that the movable member includes an elastic member elastically deformable in accordance with the movement of the fluid so that the portion of the movable member is movable with the movement of the fluid and a reaction force generated elastically in accordance with the movement of the fluid is applied to the fluid moving member. It is preferable that the fluid is a liquid.
It is preferable for generating the resonant reciprocal movement of the fluid moving member that the vibration absorber further comprises a reservoir chamber for receiving therein the fluid to be moved (that is, urged or allowed to be moved) by a first side of the fluid moving member other than a second side of the fluid moving member for moving the fluid in contact with the movable member, (that is, urging the fluid in contact with the movable member or allowing the fluid in contact with the movable member to move), and another movable member which forms at least partially the reservoir chamber and is elastically movable in accordance with the movement of the fluid in the reservoir chamber, so that a reaction force generated elastically in accordance with the movement of the fluid in the reservoir chamber is applied to the fluid moving member.
It is preferable for absorbing a large vibration amplitude that the vibration absorber includes a main chamber for receiving therein the fluid movable with a movement of the portion of the movable member, and an orifice for fluidal communication at least partially throttled between the main chamber and the reservoir chamber. It is preferable for effectively driving the fluid moving member to absorb the vibration that the vibration absorber comprises a throttle through which the fluid movable with the movement of the portion of the movable member is flowed by the fluid moving member.
The fluidal communication between the main chamber and the reservoir chamber may be prevented from being performed through the throttle. The fluidal communication between the main chamber and the reservoir chamber may be performed by the orifice and the throttle fluidly connected in series between the main chamber and the reservoir chamber, so that the size of the vibration absorber is decreased.
It is preferable for effectively driving the fluid moving member that a reciprocal movement of the fluid in the throttle resonates with the reciprocal movement of the fluid moving member. It is preferable for effectively driving the fluid moving member within a relatively wide frequency range that the driving frequency at which the fluid moving member is driven reciprocally to flow the fluid is slightly larger than a characteristic frequency of the reciprocally moving or vibrating fluid in the throttle. It is preferable for effectively moving the portion of the movable member that a vibration of the fluid in the throttle and a vibration of the fluid in the orifice harmonize with each other.
It is preferable for effectively driving the fluid moving member within the relatively wide frequency range that the characteristic frequency of the fluid moving member determined by the mass or moment of inertia of the fluid moving member and the spring constant of the reaction force is slightly larger than the characteristic vibration frequency of the fluid in the throttle.
It is preferable for restraining the motion of the fluid moving member from being disturbed by a kinetic energy of the fluid generated by the vibration of the portion of the movable member input from an outside of the vibration absorber that the vibration absorber comprises a baffle member (as denoted by a reference numeral xe2x80x9c81xe2x80x9d) between the movable member and a part of the fluid moving member at which part the fluid is moved, that is, urged or allowed to move with the movement of the portion of the movable member. The baffle member may covers the part of the fluid moving member to prevent the part of the fluid moving member from facing to the movable member in the extension and contraction directions. The baffle member may cover the part of the fluid moving member to decrease a cross-sectional area through which the part of the fluid moving member faces to the movable member in the extension and contraction directions.
The fluid moving member rotationally movable on a rotational axis may include at least two vanes for moving the fluid, that is, urging the fluid or allowing the fluid to move, and the vanes may be distant circumferentially from each other with a constant circumferential distance between the vanes adjacent to each other.
The fluid moving member may move, that is, urge an axial flow of the fluid and a radial flow of the fluid or allow the axial flow of the fluid and the radial flow of the fluid to move, at respective sides opposite circumferentially to each other on each of the vanes. It is preferable for decreasing the size of the vibration absorber that the reservoir chamber is arranged at a radially outside of the fluid moving member so that the fluid flows radially between the reservoir chamber and the fluid moving member. The reservoir chamber may extend circumferentially around the fluid moving member.
It is preferable for restraining the motion of the fluid moving member from being disturbed by the kinetic energy of the fluid generated by the vibration of the portion of the movable member input from an outside of the vibration absorber that each of the extension and contraction directions is substantially parallel to the rotational axis so that a part (radially extending vane surface) of the fluid moving member at which part the fluid is moved with the movement of the portion of the movable member is restrained from facing to the movable member in the extension and contraction directions. Each of the extension and contraction directions may be substantially perpendicular to the rotational axis.
When the vibration absorber further comprises another movable member adapted to contact with the fluid, and including a portion connected mechanically to another one of the first and second members so that a movement of the portion of the another movable member and the movement of the fluid correspond to each other, and the portions of the movable member and the another movable member move the movements of the fluid flowed by the respective vanes, the change of the distance between the portions of the movable member and the another movable member is large while the vibration absorber includes the single fluid moving member.
When the vibration absorber comprises an electromagnetic rotary actuator for driving rotationally the fluid moving member, and a torque for driving rotationally the fluid moving member is changed by changing a duty ratio of a voltage applied to the electromagnetic rotary actuator, a current amplifier for supplying a controlled electric current to the electromagnetic rotary actuator is not necessary.
It is preferable for restraining the motion of the fluid moving member from being disturbed by the kinetic energy of the fluid generated by the vibration of the portion of the movable member input from an outside of the vibration absorber that the orifice is prevented from extending straight parallel to the extension and contraction directions between the main chamber and the reservoir chamber so that the movable member and the another movable member are prevented from facing to each other through the orifice in the extension and contraction directions.